The months in the life of a Daikin 8kW install

Hardware Heatpump
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First full month has passed with our 8kW Daikin Althema HP.
We haven’t changed anything else in the house.

Thanks to the info and help from this site we’ve got things pretty much set up as we like them and economically too!

The tweaks of going LWT (with set temp set back scheduling) and getting the ECO hot water heating scheduling functioning like clockwork, have really helped our daily COPs.

Early in the month we were a bit all over the place on the Madoka, and the Comfort hot water setting really isn’t very efficient.

According to the MMI in Feb 2025 we used 510kWh for heating and hot water.

Comparing avg gas usage for previous February’s going back to 2016, we used ~1904kWh.

Ratio elec to gas 3.7.

Our total Feb bill was a bit lower than it would have been on gas!

Our gas tariff is 5.91p/kW (we fixed last year) so ~£120 for for the month Inc standing charge.
Then add our normal electricity average for Feb of ~£84
Sum £204

Our total Feb bill on the Cosy tariff is £169!
That includes £9.04 for the gas range hob, most of which is standing charge :roll_eyes:

Ok others savings we shifted dish washing and washing machine use to the cheaper Cosy times but all else remained pretty much the same.

What we’ve noticed.
The house is warmer throughout.
We’ve started heating a largish TV / hifi room annexe on steady state that previously was only heated during its use a few hours a day.
(We use it more now)

Marie (wife) and I are much happier with the constant temperature.

We can quite believe it!

Plus there’s more to come as the tweaks will improve things over the whole of the coming month!

Our months COP was 3.75.
We’ve seen it climb from mid 3s early on to mid 4s and even 6 on a warm couple of days!
It’s very weather dependant of course.

Octopus tell us
We’ve saved
1,210 kg CO2 emissions

So a huge thanks to everyone who helped answer my questions with insight and know-how, not to mention all the great info in general on this site.

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Month of march has passed by.

Cold start to the month, then with cold nights and warm days the last couple of weeks.

I’ve been turning the HP off around 9.30 to 10.00am each day and back on as needed after the peak Cosy tariff time ends at 7pm.
The solar gain we’ve been getting has been enough.

Knock back of -2C at night.

March CoP was 3.69.
Those early cold days added up.

The turning off during the day might not be the best for CoP but it seems to save the £’s vs leaving it on bouncing on and off the low LWT target.

The DHW CoPs are increasing with the warm days. 4 being the best so far.
It likes a lower tank temp to have a longer run at it but of course uses more kWs then when we’ve hardly used any hot water and it’s just topping up.

The best heating CoPs are with not to warm not to cold weather all day and night, like we had late Feb. It can just ruin end run then.

SCoP from 19th Jan to date is 3.77 (that includes the less than optimal Octopus initial settings).

(Note: All of the above are according to the Daikin MMI. Its accurate to two decimal places - not🙂)

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A lower COP does not increase running costs when the lower COP is due to needing little central heating.

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I’ve been monitoring the bills now we’re into having the heating completely off.

Gas average usage for DHW only, over the past years for these summer months was around 8.5kWh / day (gas hob usage deducted - although pretty minimal).

Since May 1st with the HP doing only DHW, I calculate it’s using

1.8kWh a day on average.

This is both looking at the Daikin MMI data and the Smart meter reporting taking our usual daily summer averages other usage into account.

Doing the DHW at 1pm with cheap Cosy tariff it’s proving nicely economical for the same DHW temp and usage pattern.

As expected, we’re pleasantly surprised by the overall electricity / gas monthly billing.
Calculating kWH usage past and present at current rates we are using / paying less.

I’ve convinced Octopus to reduce our direct debit further.

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